1. Field of the Invention
The present invention relates to isotope separation using an infrared laser for enriching the object isotope compound by selective excitation.
2. Description of the Prior Art
In general, differences of physical or chemical properties between isotope substitution products are small, especially, the differences for isotope compounds having a large molecular weight such as uranium compounds are remarkably small. Accordingly, in the conventional statistical separation for enriching the object uranium isotope compound, the change of concentration of the object isotope compound attained by one stage of the separation process is quite small and, therefore, it is necessary to repeat a large number of stages of the separation process in order to obtain the desired enriched concentration of the object uranium isotope compound. The cost for enriching the object isotope compound increases substantially in proportion to the number of stages of the separation process, which can be decreased depending upon a commensurate increase in the separation factor.
The separation factor is the ratio of relative isotopic abundance in the separation process as follows: ##EQU1## The separation factor is considered as a measure of the degree of separation in concentration in the separation process. A large separation factor makes the size of the whole facilities so small that the cost for enriching the object isotope compound can be reduced.
Various separation processes have been studied to reduce the cost for uranium isotope separation. One of these separation processes is an isotope separation using a laser wherein laser rays absorbed only by the object component in a mixture containing the isotope compounds (including isotope element) are irradiated to selectively excite the object isotope compound whereby the excited isotope compound is separated by means of a desired reaction. In principle, a large separation factor can be expected and this separation process is expected to reduce the cost for enriching the object isotope compound.
The laser isotope separation processes can be classified from the viewpoint of the wavelength of laser rays used for the selective excitation into (1) visible laser and (2) infrared laser.
In comparing visible lasers and infrared lasers for uranium isotope separation, the isotope shift of the absorbed wavelength in uranium vapor is as small as 0.08 A and the available power is small in the separation with a visible laser. Moreover, energy dissipation from the selectively excited isotope compound to another isotope compound is large because of the high exciting energy levels.
On the other hand, when the isotope compound is selectively excited with the infrared laser, the isotopic shift of the absorbed wavelength is 0.65 cm.sup.-1 in 625.5 cm.sup.-1 for the .nu..sub.3 vibration of gaseous uranium hexafluoride. The isotopic shift is about 100 times that for the visible laser and the uranium isotope compound can be more easily discriminated. Moreover, a high output laser can be used. However, the specific infrared energy is relatively small, several kcal/mole, while a conventional chemical reaction requires several tens kcal/mole. Accordingly, it is necessary to separate the selectively excited molecules by a suitable reaction.
In the past, it has been proposed to conduct the reaction in the presence of a decomposable gas. However, in this process, it is difficult to prevent direct or indirect energy transfer from the excited molecules to the molecules which should not be excited, because of collisions between gaseous molecules.